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</a></div> <!----></nav>  <ul class="sidebar-links"><li><a href="/fe/" aria-current="page" class="sidebar-link">大前端学习路径 + B站资源整合</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>CSS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>JavaScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ES6</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Vue3</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/fe/vue3/" aria-current="page" class="sidebar-link">面试官：Vue3.0的设计目标是什么？做了哪些优化</a></li><li><a href="/fe/vue3/vue3_vue2.html" class="sidebar-link">面试官：vue3有了解过吗？能说说跟vue2的区别吗？</a></li><li><a href="/fe/vue3/performance.html" class="sidebar-link">面试官：Vue3.0性能提升主要是通过哪几方面体现的？</a></li><li><a href="/fe/vue3/proxy.html" aria-current="page" class="active sidebar-link">面试官：Vue3.0里为什么要用 Proxy API 替代 defineProperty API ？</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/fe/vue3/proxy.html#一、object-defineproperty" class="sidebar-link">一、Object.defineProperty</a></li><li class="sidebar-sub-header"><a href="/fe/vue3/proxy.html#二、proxy" class="sidebar-link">二、proxy</a></li><li class="sidebar-sub-header"><a href="/fe/vue3/proxy.html#三、总结" class="sidebar-link">三、总结</a></li></ul></li><li><a href="/fe/vue3/composition.html" class="sidebar-link">面试官：Vue3.0 所采用的 Composition Api 与 Vue2.x 使用的 Options Api 有什么不同？</a></li><li><a href="/fe/vue3/treeshaking.html" class="sidebar-link">面试官：说说Vue 3.0中Treeshaking特性？举例说明一下？</a></li><li><a href="/fe/vue3/modal_component.html" class="sidebar-link">面试官：用Vue3.0 写过组件吗？如果想实现一个 Modal你会怎么设计？</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="面试官-vue3-0里为什么要用-proxy-api-替代-defineproperty-api"><a href="#面试官-vue3-0里为什么要用-proxy-api-替代-defineproperty-api" class="header-anchor">#</a> 面试官：Vue3.0里为什么要用 Proxy API 替代 defineProperty API ？</h1> <p><img src="https://static.vue-js.com/57aa5c80-5f7f-11eb-ab90-d9ae814b240d.png" alt=""></p> <h2 id="一、object-defineproperty"><a href="#一、object-defineproperty" class="header-anchor">#</a> 一、Object.defineProperty</h2> <p>定义：<code>Object.defineProperty()</code> 方法会直接在一个对象上定义一个新属性，或者修改一个对象的现有属性，并返回此对象</p> <h5 id="为什么能实现响应式"><a href="#为什么能实现响应式" class="header-anchor">#</a> 为什么能实现响应式</h5> <p>通过<code>defineProperty</code> 两个属性，<code>get</code>及<code>set</code></p> <ul><li>get</li></ul> <p>属性的 getter 函数，当访问该属性时，会调用此函数。执行时不传入任何参数，但是会传入 this 对象（由于继承关系，这里的this并不一定是定义该属性的对象）。该函数的返回值会被用作属性的值</p> <ul><li>set</li></ul> <p>属性的 setter 函数，当属性值被修改时，会调用此函数。该方法接受一个参数（也就是被赋予的新值），会传入赋值时的 this 对象。默认为 undefined</p> <p>下面通过代码展示：</p> <p>定义一个响应式函数<code>defineReactive</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    app<span class="token punctuation">.</span>innerText <span class="token operator">=</span> obj<span class="token punctuation">.</span>foo
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">defineReactive</span><span class="token punctuation">(</span><span class="token parameter">obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> val</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        <span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">get </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>val<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token keyword">return</span> val
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">set</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>newVal <span class="token operator">!==</span> val<span class="token punctuation">)</span> <span class="token punctuation">{</span>
                val <span class="token operator">=</span> newVal
                <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>调用<code>defineReactive</code>，数据发生变化触发<code>update</code>方法，实现数据响应式</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
<span class="token function">defineReactive</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">,</span> <span class="token string">''</span><span class="token punctuation">)</span>
<span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
    obj<span class="token punctuation">.</span>foo <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">toLocaleTimeString</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">,</span><span class="token number">1000</span><span class="token punctuation">)</span>
</code></pre></div><p>在对象存在多个<code>key</code>情况下，需要进行遍历</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">observe</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> obj <span class="token operator">!==</span> <span class="token string">'object'</span> <span class="token operator">||</span> obj <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span>
    <span class="token punctuation">}</span>
    Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">key</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
        <span class="token function">defineReactive</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> obj<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>如果存在嵌套对象的情况，还需要在<code>defineReactive</code>中进行递归</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">defineReactive</span><span class="token punctuation">(</span><span class="token parameter">obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> val</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">observe</span><span class="token punctuation">(</span>val<span class="token punctuation">)</span>
    Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        <span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">get </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>val<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token keyword">return</span> val
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">set</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>newVal <span class="token operator">!==</span> val<span class="token punctuation">)</span> <span class="token punctuation">{</span>
                val <span class="token operator">=</span> newVal
                <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>当给<code>key</code>赋值为对象的时候，还需要在<code>set</code>属性中进行递归</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">set</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>newVal <span class="token operator">!==</span> val<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">observe</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span> <span class="token comment">// 新值是对象的情况</span>
        <span class="token function">notifyUpdate</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>上述例子能够实现对一个对象的基本响应式，但仍然存在诸多问题</p> <p>现在对一个对象进行删除与添加属性操作，无法劫持到</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
    foo<span class="token operator">:</span> <span class="token string">&quot;foo&quot;</span><span class="token punctuation">,</span>
    bar<span class="token operator">:</span> <span class="token string">&quot;bar&quot;</span>
<span class="token punctuation">}</span>
<span class="token function">observe</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span>
<span class="token keyword">delete</span> obj<span class="token punctuation">.</span>foo <span class="token comment">// no ok</span>
obj<span class="token punctuation">.</span>jar <span class="token operator">=</span> <span class="token string">'xxx'</span> <span class="token comment">// no ok</span>
</code></pre></div><p>当我们对一个数组进行监听的时候，并不那么好使了</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> arrData <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
arrData<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">val<span class="token punctuation">,</span>index</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
    <span class="token function">defineProperty</span><span class="token punctuation">(</span>arrData<span class="token punctuation">,</span>index<span class="token punctuation">,</span>val<span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
arrData<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// no ok</span>
arrData<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token punctuation">)</span>  <span class="token comment">// no ok</span>
arrDate<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">99</span> <span class="token comment">// ok</span>
</code></pre></div><p>可以看到数据的<code>api</code>无法劫持到，从而无法实现数据响应式，</p> <p>所以在<code>Vue2</code>中，增加了<code>set</code>、<code>delete</code> API，并且对数组<code>api</code>方法进行一个重写</p> <p>还有一个问题则是，如果存在深层的嵌套对象关系，需要深层的进行监听，造成了性能的极大问题</p> <h3 id="小结"><a href="#小结" class="header-anchor">#</a> 小结</h3> <ul><li>检测不到对象属性的添加和删除</li> <li>数组<code>API</code>方法无法监听到</li> <li>需要对每个属性进行遍历监听，如果嵌套对象，需要深层监听，造成性能问题</li></ul> <h2 id="二、proxy"><a href="#二、proxy" class="header-anchor">#</a> 二、proxy</h2> <p><code>Proxy</code>的监听是针对一个对象的，那么对这个对象的所有操作会进入监听操作，这就完全可以代理所有属性了</p> <p>在<code>ES6</code>系列中，我们详细讲解过<code>Proxy</code>的使用，就不再述说了</p> <p>下面通过代码进行展示：</p> <p>定义一个响应式方法<code>reactive</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> obj <span class="token operator">!==</span> <span class="token string">'object'</span> <span class="token operator">&amp;&amp;</span> obj <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> obj
    <span class="token punctuation">}</span>
    <span class="token comment">// Proxy相当于在对象外层加拦截</span>
    <span class="token keyword">const</span> observed <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        <span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">获取</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>res<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">设置</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>value<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">deleteProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> key</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">deleteProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">删除</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>res<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> observed
<span class="token punctuation">}</span>
</code></pre></div><p>测试一下简单数据的操作，发现都能劫持</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> state <span class="token operator">=</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    foo<span class="token operator">:</span> <span class="token string">'foo'</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token comment">// 1.获取</span>
state<span class="token punctuation">.</span>foo <span class="token comment">// ok</span>
<span class="token comment">// 2.设置已存在属性</span>
state<span class="token punctuation">.</span>foo <span class="token operator">=</span> <span class="token string">'fooooooo'</span> <span class="token comment">// ok</span>
<span class="token comment">// 3.设置不存在属性</span>
state<span class="token punctuation">.</span>dong <span class="token operator">=</span> <span class="token string">'dong'</span> <span class="token comment">// ok</span>
<span class="token comment">// 4.删除属性</span>
<span class="token keyword">delete</span> state<span class="token punctuation">.</span>dong <span class="token comment">// ok</span>
</code></pre></div><p>再测试嵌套对象情况，这时候发现就不那么 OK 了</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> state <span class="token operator">=</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    bar<span class="token operator">:</span> <span class="token punctuation">{</span> a<span class="token operator">:</span> <span class="token number">1</span> <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>

<span class="token comment">// 设置嵌套对象属性</span>
state<span class="token punctuation">.</span>bar<span class="token punctuation">.</span>a <span class="token operator">=</span> <span class="token number">10</span> <span class="token comment">// no ok</span>
</code></pre></div><p>如果要解决，需要在<code>get</code>之上再进行一层代理</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> obj <span class="token operator">!==</span> <span class="token string">'object'</span> <span class="token operator">&amp;&amp;</span> obj <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> obj
    <span class="token punctuation">}</span>
    <span class="token comment">// Proxy相当于在对象外层加拦截</span>
    <span class="token keyword">const</span> observed <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        <span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">获取</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>res<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> <span class="token function">isObject</span><span class="token punctuation">(</span>res<span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token function">reactive</span><span class="token punctuation">(</span>res<span class="token punctuation">)</span> <span class="token operator">:</span> res
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token keyword">return</span> observed
<span class="token punctuation">}</span>
</code></pre></div><h2 id="三、总结"><a href="#三、总结" class="header-anchor">#</a> 三、总结</h2> <p><code>Object.defineProperty</code>只能遍历对象属性进行劫持</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">observe</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> obj <span class="token operator">!==</span> <span class="token string">'object'</span> <span class="token operator">||</span> obj <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span>
    <span class="token punctuation">}</span>
    Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">key</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
        <span class="token function">defineReactive</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> key<span class="token punctuation">,</span> obj<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>Proxy</code>直接可以劫持整个对象，并返回一个新对象，我们可以只操作新的对象达到响应式目的</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> obj <span class="token operator">!==</span> <span class="token string">'object'</span> <span class="token operator">&amp;&amp;</span> obj <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> obj
    <span class="token punctuation">}</span>
    <span class="token comment">// Proxy相当于在对象外层加拦截</span>
    <span class="token keyword">const</span> observed <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        <span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">获取</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>res<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">设置</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>value<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token function">deleteProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> key</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> res <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">deleteProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">)</span>
            console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">删除</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">:</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>res<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> res
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> observed
<span class="token punctuation">}</span>
</code></pre></div><p><code>Proxy</code>可以直接监听数组的变化（<code>push</code>、<code>shift</code>、<code>splice</code>）</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> obj <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">]</span>
<span class="token keyword">const</span> proxtObj <span class="token operator">=</span> <span class="token function">reactive</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span>
obj<span class="token punctuation">.</span><span class="token function">psuh</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span> <span class="token comment">// ok</span>
</code></pre></div><p><code>Proxy</code>有多达13种拦截方法,不限于<code>apply</code>、<code>ownKeys</code>、<code>deleteProperty</code>、<code>has</code>等等，这是<code>Object.defineProperty</code>不具备的</p> <p>正因为<code>defineProperty</code>自身的缺陷，导致<code>Vue2</code>在实现响应式过程需要实现其他的方法辅助（如重写数组方法、增加额外<code>set</code>、<code>delete</code>方法）</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// 数组重写</span>
<span class="token keyword">const</span> originalProto <span class="token operator">=</span> <span class="token class-name">Array</span><span class="token punctuation">.</span>prototype
<span class="token keyword">const</span> arrayProto <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">create</span><span class="token punctuation">(</span>originalProto<span class="token punctuation">)</span>
<span class="token punctuation">[</span><span class="token string">'push'</span><span class="token punctuation">,</span> <span class="token string">'pop'</span><span class="token punctuation">,</span> <span class="token string">'shift'</span><span class="token punctuation">,</span> <span class="token string">'unshift'</span><span class="token punctuation">,</span> <span class="token string">'splice'</span><span class="token punctuation">,</span> <span class="token string">'reverse'</span><span class="token punctuation">,</span> <span class="token string">'sort'</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">method</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  arrayProto<span class="token punctuation">[</span>method<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    originalProto<span class="token punctuation">[</span>method<span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>arguments<span class="token punctuation">)</span>
    dep<span class="token punctuation">.</span><span class="token function">notice</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// set、delete</span>
Vue<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span><span class="token string">'bar'</span><span class="token punctuation">,</span><span class="token string">'newbar'</span><span class="token punctuation">)</span>
Vue<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token string">'bar'</span><span class="token punctuation">)</span>
</code></pre></div><p><code>Proxy</code> 不兼容IE，也没有 <code>polyfill</code>, <code>defineProperty</code> 能支持到IE9</p> <h3 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h3> <ul><li>https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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